1. Field of the Invention
The present invention relates to a scroll compressor used for an apparatus such as a refrigerator, an air conditioner and so on in which a refrigerant is compressed.
2. Discussion of Background
Before discussing the present invention, the principle of the scroll type fluid transferring machine will be briefly described.
FIG. 2 shows the major structural elements and the principle of compression when a scroll type fluid transferring machine is used as a compressor.
In FIG. 2, a reference numeral 1 designates a stationary scroll, a numeral 2 designates an orbiting scroll, a numeral 3 designates an intake chamber, a numeral 4 designates a discharge port and a numeral 5 designates a compression chamber. A symbol O represents the center of the stationary scroll 1.
The stationary and orbiting scrolls 1, 2 respectively have a wrap plate 1a or 2a. The wrap plates 1a, 2a have the same shape but the winding direction of the wrap plates is opposite. They are constituted by involute curves or a combination of curved lines.
The operation of the scroll type fluid trasferring machine will be described. The stationary scroll 1 stands still in space, and the orbiting scroll 2 is combined with the stationary scroll 1 with a phase deviated from 180.degree. so that the orbiting scroll 2 undergoes the movement of revolution but not rotation around the center of the stationary scroll 1. FIGS. 2a to 2d show each state of the stationary and orbiting scrolls 1, 2 at angle positions of 0.degree., 90.degree., 180.degree. and 270.degree.. FIG. 2a shows the state of the angle position of 0.degree. at which enclosure of a fluid in the intake chamber 3 is finished and the compression chamber 5 is formed between the wrap plates 1a, 2a. As the orbiting scroll 2 rotates, the volume of the compression chamber 5 gradually decreases to compress the fluid, and finally the compressed fluid is discharged through the discharge port 4 formed at the center of the stationary scroll 1.
In the next place, the construction and the operation of the scroll compressor will be described. FIG. 3 shows a typical construction of the scroll compressor as disclosed, for instance, in Japanese Patent Application No. 64571/1984, in which the scroll compressor is used for a totally closed type refrigerant compressor.
In FIG. 3, the wrap plate la of the stationary scroll 1 is formed on a surface of the base plate 1b. The orbiting scroll 2 comprises the wrap plate 2a formed on a surface of the base plate 2b and a scroll shaft 2c formed on the other surface of the base plate 2b. The intake chamber (intake port) 3 and the compression chamber 5 are formed by combining the wrap plates 1a, 2a of the stationary and orbiting scrolls 1, 2 as described above.
A reference numeral 6 designates a main shaft, a numeral 7 designates an oil cap having an intake port 7a which is attached to the lower portion of the main shaft 6 so as to cover the lower portion with a predetermined space, numerals 8, 9 designate bearing supporters, a numeral 10 designates the rotor of an electric motor, a numeral 11 designates the stator of the motor, a numeral 12 designates a shell containing the structural elements of the scroll compressor, a numeral 13 designates an Oldham coupling, a numeral 14 designates an obstacle plate, a numeral 15 designates an oil reservoir formed in the bottom of the shell. A fluid intake pipe 16 and a discharge pipe 17 are respectively mounted on the shell 12 so as to pass through it.
The main shaft 6 has an enlarged diameter portion 6a at its upper part in which an eccentric cylindrical recess 6d is formed in the upper surface of the large diameter portion at a position deviated from the axial center of the main shaft. The scroll shaft 2c of the orbiting scroll 2 is received in the eccentric recess 6d. An orbiting scroll bearing 18 is fitted between the outer circumferential surface of the scroll shaft 2c and the inner surface of the eccentric recess 6d in a freely rotatable manner. A space 6e is formed between the lower end of the scroll shaft 2c and the bottom of the eccentric recess 6d. A first main bearing 19 is placed on the outer circumferential surface of the large diameter portion 6a of the main shaft 6 to rotatably support the main shaft 6. A second main bearing 20 supports a small diameter portion 6b at the lower part of the main shaft 6. A thrust bearing 21 supports the lower surface of the base plate 2b as a sliding surface 2d of the orbiting scroll 2 in the axial direction. A second thrust bearing 22 supports a step portion 6c formed at the boundary between the large diameter portion 6a and the small diameter portion 6b of the main shaft 6 in the axial direction. An oil feeding passage 23 extends in the main shaft 6 at a position deviated from the axial center so as to communicated with each of the bearings 18 to 20. In FIG. 3, a reference numeral 24 designates a gas-vent hole formed in he main shaft 6, numerals 25, 26 designate oil returning openings and numerals 27, 28 designate communicating openings which allow the intake gas to pass therethrough.
In the conventional scroll compressor, the orbiting scroll 2 is combined with the stationary scroll 1; the scroll shaft 2c is engaged with the main shaft 6 by means of the scroll bearing 18, and the orbiting scroll 2 is supported by the main shaft 6 through the scroll bearing 18 and the first thrust bearing 21 mounted on the bearing supporter 8.
The main shaft 6 is supported in the shell 12 by means of the first main bearing 19 provided in the bearing supporters 8, 9, the second main bearing 20 and the second thrust bearing 22. The Oldham coupling 13 is provided between the orbiting scroll 2 and the bearing supporter 8 to prevent the orbiting scroll 2 to rotate around its axial center but to allow it to have only a movement of revolution. After the above-mentioned elements are preliminarily assembled, the stationary scroll 1 is fastened to the bearing supporters 8, 9 by means of bolts. The rotor 10 is fixed to the main shaft and the stator 11 is fixed to the bearing supporter 9 by forcibly inserting, stake-fitting or screwing. The oil cap 7 is fixed to the main shaft 6 by the forcibly inserting or stake-fitting. The assembled elements are together received in and fixed to the interior of the shell 12 with the stationary and orbiting scrolls 1, 2 directing upward while the rotor 10 and the stator 11 located downward. The entire assembly is fixed to the shell by the forcible-insertion or the stake-fitting.
The operation of the conventional scroll compressor having the construction as mentioned above will be described.
On starting actuation of the rotor 10 of the motor, the revolution of the orbiting scroll 2 is initiated by means of the main shaft 6 and the Oldham coupling 1, whereby compression of the gas is initiated by the principle of operation as described with reference to FIG. 2. The refrigerant gas is sucked into the shell 12 through the intake pipe 16. The gas is passed through the communicating opening 27 formed between the bearing supporter 9 and the stator 11 of the motor, and the air gap formed between the rotor 10 and the stator 11 as indicated by solid lines, while the refrigerant gas cools the motor. Then, the gas is passed through the communicating opening 28 formed bewtween the shell 12 and the bearing supporters 8, 9, and is taken into the compression chamber 5 through the intake port 3 formed in the stationary scroll 1 so as to be compressed. The compressed gas is discharged outside the compressor via the discharge port 4 and the discharge pipe 17.
The lubricating oil is sucked into the oil feeding passage 23 by the action of centrifugal pumping function which is given by the oil cap and the oil feeding passage 23 formed in the main shaft 6. The lubricating oil is fed through the oil feeding passage 23 from the intake port 7a of the oil cap 7 to the space 6e in the eccentric recess 6d from which the lubricating oil is supplied to each of the bearings 18, 20 and then, is supplied to the bearings 21, 19, 22 in this order, as indicated by broken arrow marks. After lubrication to the bearings, the lubricating oil is returned to the oil reservoir 15 after it is mainly passed through the oil returning openings 25, 26 which are respectively formed in the bearing supporters 8, 9. The obstacle plate 14 is provided to close an air gap between the bearing supporter 8 and the outer circumferential surface of the orbiting scroll 2 so that a part of the lubricating oil leaked from the bearing 21 is not directly sucked into the intake port 3 (intake chamber). The obstacle plate 14 separates the intake port 3 (intake chamber) from the movable parts of the compressor in association with the orbiting scroll 2. The gas-vent hole 24 formed in the main shaft 6 has such function that gas in the oil cap 7 is rapidly discharged out of the main shaft when the scroll compressor is operated to thereby increase efficiency of pump.
In the conventional scroll compressor, when the lubricating oil sucked through the oil cap 7 flows in the oil feeding passage 23 of the main shaft 6 and flows in the space 6e in the eccentric recess 6d, the lubricating oil is splashed to the bearing 18 of the orbiting scroll 2 due to the centrifugal force. Especially, when the scroll compressor is used for a refrigerant compressor, the refrigerant is mixed or dissolved in the lubricating oil, whereby foaming and gasification of the refrigerant take place. The gasification of the refrigerant is caused by the two reasons as follows. First, in an oil passage extending from the inlet of the oil feeding passage 23 to the bearing 18, the oil pressure is the lowest at the exit of the oil feeding passage 23 which opens the eccentric recess 6d. Second, the temperature of the bearings 18, 19, the temperature of a working fluid subjecting to compression according to the principle of compression which is described above and the temperature of the central part of the base plate 2b of the orbiting scroll and the elements located nearby the base plate 2b become higher than the other parts. Then, the lubricating oil is heated by these elements having elevated temperatures while it is fed through the space 6e in the eccentric recess 6d and the bearings 18, 19, 20. When the foamed refrigerant gas is filled in the space 6e, or oil grooves formed in the bearings 18, 19, or a space defined by the upper end surface of the main shaft 6, the lower surface of the base plate of the orbiting scroll 2 and the inner circumferential surface of the thrust bearing 20, there takes place difference in pressure between the space 6e in the eccentric recess 6d and the upper space. For instance, when the pressure of the upper space is higher than that of the space 6e of the eccentric recess, namely, when the oil pressure at the downstream side of the oil feeding passage is higher than that of the upstream side, an oil flow is stopped. Further, since the lubricating oil having foams imparts a large resistance in flow in the oil groove in comparison with the lubricating oil without having the foams, it is difficult to cause a smooth oil flow. Accordingly, there causes locally short of oil supply, whereby the bearings may be damaged, or seizure of the bearings sometimes occurs.